Isomerization and reorientation of Disperse Red 1 in poly(ethyl methacrylate)

Irradiation of azobenzene-containing polymer materials with light causes cis-trans isomerization and reorientation of azobenzene moieties and thereby changes in the optical properties of the materials. In this study, the film of poly(ethyl methacrylate) doped with the azobenzene derivative Disperse Red 1 (DR1) has been irradiated with the linearly polarized light of 546 nm. The time profiles of optical anisotropy and absorbance measured during irradiation have been analyzed using a kinetic model. Based on the analysis of the time profiles, we conclude that the light-induced reorientation of DR1 molecules occurs in confined environments where trans → cis isomerization is hindered, while in roomy environments, there is no reorientation. In the confined environment, reorientation occurs due to the environmental changes caused by the isomerization attempts of the DR1 molecule. The polymer environment affects thermal cis → trans and light-induced trans → cis isomerizations of the DR1 molecule differently, suggesting that the spatial requirements for these processes to proceed are different. The thermal isomerization does not result in the reorientation of DR1 molecules in roomy environments.